import java.util.*;
public class  test04 
{
	static long fibonacci(int nIn){
    long aIn = 1;
	long bIn = 1;
	long cIn = 1;
	for(int i=1;i<=nIn;i++){
		cIn=aIn;
		aIn=aIn+bIn;
		bIn=cIn;}
	return aIn;}
	public static void main(String[] args) 
	{
		int n;
		long a;
		Scanner sc=new Scanner(System.in);
        n=sc.nextInt();
		a=fibonacci(n);
   		System.out.println(a);
	}
}
